Studies encompass the physiology, behavior, genetics, and vector competence of anopheline mosquitoes, the vectors of malaria. Techniques of transplantation and perfusion have been used to study the fate of sporozoites released from oocysts growing in both refractory and susceptible mosquitoes. Plasmodium knowlesi sporozoites produced in the refractory Anopheles freebroni will not invade the An. freeborni salivary glands but will invade those of the susceptible Anopheles balabacensis. Sporozoites which do not invade salivary tissue are destroyed equally quickly in both refractory and susceptible species. Growth and reproduction in mosquitoes and reduvid bugs has been diminished by feeding these insects blood containing antibodies to their gut secretions. Some functional immunoglobulin also traverses the gut barrier into the hemolymph. Isoenzyme and biological studies have helped separate two natural populations of An. balabacensis that may be different species of unequal vectorial capacity. The genetic and physiological basis for vector competence is also being investigated in An pharoensis and An gambiae.